Exposure to blue light, via regular use of tablets and smartphones, may alter hormone levels and increase the risk of earlier puberty, according to data from a rat study presented today at the 60th Annual European Society for Paediatric Endocrinology Meeting. Longer duration of blue light exposure was associated with earlier puberty onset in the female rats, which also showed reduced levels of melatonin, increased levels of some reproductive hormones and physical changes in their ovaries. Use of blue-light emitting mobile devices has previously been linked to disrupted sleeping patterns in children but these findings suggest there could be additional risks for childhood development and future fertility.
The escalating use of blue light emitting devices, such as tablets and smartphones, has previously been implicated in reducing sleep quality in both children and adults. This is thought to be through disruption of our body clock as blue light inhibits the evening rise in levels of the hormone, melatonin, which prepares our bodies for rest and sleep. Melatonin levels are overall higher during pre-puberty than in puberty, which is believed to play a role in delaying the start of puberty. Puberty is a complex process that involves co-ordination of several body systems and hormones.
In recent years, several studies have reported increases in early puberty onset for girls, particularly during the COVID-19 pandemic. The link between blue light exposure and reduced melatonin levels suggests that increased screen time, such as during the pandemic restrictions, may be playing a role in this reported increase. However, it is very difficult to assess this in children.
In this study, Dr Aylin Kilinç Uğurlu and colleagues in Ankara, Turkey, used a rat model to investigate the effects of blue light exposure on reproductive hormone levels and the time of puberty onset. Female rats were divided into three groups of six and exposed to either a normal light cycle, 6 hours or 12 hours of blue light. The first signs of puberty occurred significantly earlier in both groups exposed to blue light, and the longer the duration of exposure, the earlier the onset of puberty. Rats exposed to blue light also had reduced melatonin levels and elevated levels of specific reproductive hormones (oestradiol and luteinising hormone), as well as physical changes in their ovarian tissue, all consistent with puberty onset. At the 12 hours exposure, rats also showed some signs of cell damage and inflammation in their ovaries.
Dr Aylin Kilinç Uğurlu comments, “We have found that blue light exposure, sufficient to alter melatonin levels, is also able to alter reproductive hormone levels and cause earlier puberty onset in our rat model. In addition, the longer the exposure, the earlier the onset.”
Although Dr Aylin Kilinç Uğurlu , cautions, “As this a rat study, we can’t be sure that these findings would be replicated in children but these data suggest that blue light exposure could be considered as a risk factor for earlier puberty onset.”
It is difficult to mimic blue light exposure equivalent to a child’s tablet use in rats but the time-point of puberty in rats is roughly equivalent to that of humans, if adjusted for rats’ lower life expectancy. The hormonal and ovulation changes that occur during pre-puberty and puberty in female rats are also comparable to humans. So, despite the study limitations these findings support further investigation of the potential health impacts of blue light exposure on hormone levels and puberty onset in children.
The team plans to investigate the cell damage and inflammatory effects detected after longer blue light exposure, since this could have long-term impacts on reproductive health and fertility. They will also assess whether the use of blue light minimising ‘night light’ mobile device features can reduce the effects observed in the rat model.
Dr Aylin Kilinç Uğurlu adds, “Although not conclusive, we would advise that the use of blue light emitting devices should be minimised in pre-pubertal children, especially in the evening when exposure may have the most hormone-altering effects.”
Blue Light Exposure and Exposure Duration Effects on Rats' Puberty Process
Aylin Kılınç Uğurlu1, Aysun Bideci2, Ayşe Mürşide Demirel3, Gülnur Take Kaplanoğlu4, Duygu Dayanır4, Özlem Gülbahar5, Tuba Saadet Deveci Bulut5, Esra Döğer2, M. Orhun Çamurdan2
1Ankara City Hospital, Pediatric Endocrinology Clinic, Ankara, Turkey. 2Gazi University Faculty of Medicine, Department of Pediatric Endocrinology, Ankara, Turkey. 3Gazi University Faculty of Pharmacy, Laboratory Animals Breeding and Experimental Research Center, Ankara, Turkey. 4Gazi University Faculty of Medicine, Department of Histology and Embryology, Ankara, Turkey. 5Gazi University Faculty of Medicine, Department of Medical Biochemistry, Ankara, Turkey
Introduction: In the last 10 years, blue light (BL) sources such as tablets and phones has increased in every age group. Especially due to the Covid-19 pandemic, screen exposure has also increased in childhood. However, the effects of BL exposure in the puberty process aren’t clear. We aimed to examine the effect of BL exposure and exposure time on puberty.
Methods: Immature eighteen 21-day-old female Sprague Dawley rats were divided into three groups consisting of six rats in each group: Control Group (CG), Experiment Group-1 (EG-1), Experiment Group-2 (EG-2). CG rats were maintained under standard conditions with 12/12-hour light-dark cycles . The rats of EG-1 and EG-2 were exposed to BL (450-470 nm / irradiance level 0.03 uW/cm2) for 6 hours and 12 hours, respectively. Rats were exposed to BL until the first signs of puberty and then they were euthanasiad. Serum FSH, LH, Estrodiol, testosterone, DHEA-S, leptin, melatonin were studied by ELISA method. Ovaries and uterus were dissected for histomorphological examination
Results: The medians of the pubertal entry days of the CG, EG-1 and EG-2 were 38th, 32nd, and 30th days, respectively. (p: 0.001) A negative correlation was found between the puberty entry day of the groups and the exposure to BL and the duration of exposure. (r:-0.910, p<0.001)
The FSH, testosterone, DHEA-S, leptin levels of all groups were similar. (p> 0.05) However, LH and estradiol levels of EG-1 were higher compared CG. (p:0.027) There was a negative correlation between BL exposure, exposure time and melatonin levels (ro:- 0.537, p: 0.048) Ovarian tissue was compatible with pubertal period in all groups. As the BL exposure time increased, capillary dilatation and edema in the over tissue increased. Prolonged exposure caused polycystic over like (PCO-like) morphological changes and apoptosis in granulosa cells.
Conclusion: Our study is the first to show the effects of BL exposure on puberty. In our study, we showed that exposure of BL and the duration of exposure lead to early puberty. PCO-like, inflammation and apoptosis were detected in the ovaries with the increase in BL exposure time.
There are studies showing that there is an increase in cases with precocious puberty and acceleration in puberty pace during the closure period compared to the pre-pandemic period. In our study, we experimentally demonstrated the effects of BL exposure on puberty and the relationship between increased exposure time.